1. Field of the Invention
The present invention relates to a tire monitoring device and system capable of automatically locating a tire.
2. Discussion of Related Art
In general, a tire monitoring system (TMS) is a safety apparatus enabling continuous monitoring of pressure, temperature, etc. of tires during operation of a vehicle. The TMS is intended to measure variables such as pressure and temperature of tires, and warn the driver to remove a dangerous factor and ensure safety when the variables indicate an abnormal state. Such a TMS generally has a sensor device installed in each wheel of a vehicle and including a microprocessor and a radio frequency (RF) transmitter, and a central control unit including an RF receiver connected with an antenna.
However, when tire exchange or replacement is performed, it is very troublesome and takes much time to register the changed state in the central control unit, and also an input error may ruin the safety function. Thus, when a tire exchange or tire replacement event occurs, it is preferred to automatically detect the event and automatically identify and register the position of a tire, which is referred to as auto-location.
In the case of a car, a pair of accelerometers measuring accelerations in orthogonal directions is generally installed to determine whether a vehicle wheel is on the left or right side on the basis of a phase difference between sine waves of measured acceleration values caused by the acceleration of gravity. Such a method has been fully disclosed in U.S. Patent Laid-Open Publication No. 2006/0044125, U.S. Pat. No. 6,204,758.
However, a sensor device including an acceleration sensor generally operates on a built-in battery, and continuous auto-location and signal transmission shorten battery life. Furthermore, auto-location is not needed in normal times except immediately after a tire exchange (sometimes called “tire rotation”) event or tire replacement event (collectively “tire event”), and rather, continued auto-location may generate a mis-recognition due to an erratic driving environment or noise. Thus, it is necessary to perform auto-location only when needed and to suppress operation for auto-location in a sleep mode to prevent unnecessary battery consumption.